1. Field of the Invention
This invention relates generally to method and system for calculating rod average criteria in a nuclear reactor.
2. Description of Related Art
Operating nuclear plants have to conform to regulatory board guidelines for evaluating radiological consequences of design basis accidents. These guidelines provide guidance to licensees of operating power reactors on acceptable applications of Alternative Source Terms (AST); the scope, nature, and documentation of associated analyses and evaluations; consideration of impacts on analyzed risk; and content of submittals. The guidelines establish an acceptable AST and identify the significant attributes of other ASTs that may be found acceptable by the U.S. Nuclear Regulatory Commission (NRC). The guidelines also identify acceptable radiological analysis assumptions for use in conjunction with the accepted AST. The NRC mandates these guidelines in 10 CFR Part 50 documentation, particularly, 10 CFR 50.67 which describes the AST methodology characterized by radionuclide composition and magnitude, chemical and physical form of the nuclides, and the timing of release of these radionuclides. As part of the AST methodology, the inventory of fission products in the reactor core and availability of release to the containment may be determined to be acceptable for use with currently approved fuel. These values are evaluated to determine whether they are consistent with the safety margins, including margins to account for analysis uncertainties. The safety margins are products of specific values and limits contained in the technical specifications (which cannot be changed without NRC approval) and other values, such as assumed accident or transient initial conditions or assumed safety system response times. As an example, fractions of fission product inventory for fuel with a peak exposure up to, for example, 62,000 MWD/MTU (Mega Watt-Days per metric ton of Uranium) may be evaluated, if the maximum linear heat generation rate does not exceed 6.3-kW/ft (kilo-Watt per feet) peak rod average power for exposures exceeding 54,000 MWD/MTU. In other words, the AST methodology basis may simplify the acceptance criterion, (i.e., if the peak rod average exposure exceeds 54,000 MWD/MTU, then the rod's average linear heat generation rate cannot exceed 6.3 kW/ft). Further, fission gas release calculations should be performed using approved methodologies, and the U.S. NRC may consider the methodology on a case-by-case basis. However, current AST methodologies do not have a manner in showing compliance of criterion during the design, optimization, licensing, and/or monitoring phases because current methodologies fail to directly calculate the constraint. In other words, to obtain the criterion of the rods, one may need to manipulate data that is external to the design, optimization, licensing, and/or monitoring phases, which may be a time-consuming and laborious process. Further, conservative assumptions may be employed to determine the criteria, however, this procedure may provide inaccurate criteria, which may adversely impact plant operations.